1. Field of the Invention
The present invention is related to an electromagnetic pump, and particularly to an electromagnetic pump of the type in which a fluid is sucked and discharged by reciprocating a piston using the attracting action of an electromagnet and the repulsive action of a spring means.
2. Description of the Prior Art
Publicly known is an electromagnetic pump of the type in which a piston head placed for sliding in a cylinder and having a piston is biased in one direction by a spring and the piston is periodically attracted in the direction opposite to the above direction using an electromagnet to repetitively such and discharge a fluid.
Attached to the piston is an armature which is formed by laminating a plurality of doughnut-like plates of a magnetic material. The piston is cast after the armature is fitted into the mold of the piston.
The electromagnet for attracting the armature constitutes of a pair of magnetic poles placed outside the armature, a field core of a hollow, rectangular material placed around the armature, and coils wound around the magnetic poles.
In the conventional electromagnetic pump described above, the electromagnet for attracting the armature has a large size and heavy weight, and as a result, the electromagnetic pump is also large-sized and heavy. The reason for this is as follows:
(1) The spring means and shaft for biasing the piston in one direction are disposed so that the end portions of them are adjacent to the armature, the end portions are positioned close to or within the magnetic gaps between the armature and the magnetic poles of the field core, and the magnetic path is long. Thus, the magnetic fluxes generated in the electromagnet are susceptible to leakage.
The spring means may be remotely positioned to prevent the magnetic leakage, but it may cause a large-size and heavy weight of the moving portion. In addition, the spring means may be formed of non-magnetic materials such as stainless wire, but these materials are not preferred because they have unstable mechanical properties and a small stress of shear strength. Accordingly, the spring means should be formed using a magnetic material which has unstable mechanical properties and a large allowable stress or shear strength (e.g. steel for spring), but in this case, the magnetic leakage becomes large and it is required to increase the magnetomotive force (ampereturns) of the coils to be wound around the magnetic poles or field core.
(2) In the conventional electromagnetic pump as discussed above, a field core having magnetic poles is a hollow, rectangular material and it is placed outside an armature so as to surround the armature, and thus the field core is large-sized. Consequently, the amount of the magnetic material constituting the field core and armature will increase.
Since the rectangular field core results in a relatively long magnetic path and also a large magnetic leakage, it is required to increase the magnetomotive force of the coils to be wound around the field core.